The minimum bogie count that should be officially recognized and was not supported is 3 since I did test a locomotive with 3 bogies and there was a comment from a post that mentioned MSTS does support 3 bogies. I then added one more to make it 4 since doing so does not require major code change.
The default axles tested for and added is currently 3 per bogie, but the last test will add any additional axles not specifically tested for.